if the EWS is not blocking the windows or sunroof, the error must not be in the EWS alone. My guess is a short in one of the door wiring looms.
I'll check these next week. Thank you very much for all the help and ideas you already provided.

I don't think those error codes are much to worry about, except the first 255 error- that may, or may not, represent something very strange: Mostly likely an 'undefined or unexpected' problem, as you may well know. If it has EWS- so uses a transponder key/RF ring around the ignition barrel, the last two errors may be saying the car does not recognise the code. Have you tried programming the key to one of the 10 key memories? In DIS, you can see each one used, was your key shown in the list of keys trusted by the EWS/ECU? I suspect your root cause is actually preventing power to the second module/antitheft box under the rear seat, amongst other things around the GM. But the antitheft module was an optional feature, so yours may not have it. Either way, power from the rear distribution unit/GM/antitheft probably goes to the OBC and EWS module with the blue connector beside the steering column, beside the knee bolster. This disables the starter motor and the ECM from running fuel and spark, IIRC. But not windows etc.

When was yours built? IIRC, EWS II is 6/95 (depends on production/market). Are you sure yours has EWS? Is it EWS I or EWS II? If so there is a module under the dash. Supplying power to one of its pins allows the engine to start.

What diagnosis tool did you use? BMW EasyDIS is very good for e34 via the ADS interface.

Have you verified the body electronics (50A) in line fuse is not hairline cracked/rusted/blown? This is not by the battery, it's under the rear footwell carpet, drivers side on a LHD V8.

One solution is to strip the seats and carpet out get a new body wiring harness from a good e34 (same build/same options) and fit that, or at least to replace the left side and everything around the rear power distribution box. Repairing the cracked/oxidised wires is fraught with pain- there are so many small connections. How is the state of the power distribution connectors, especially the GM ones, under it? If oxidised around the pins, resistance can build up down the wire (water can seep down each wire around the copper strands a long way, causing oxidisation and resistance which may be a root cause for a failing GM or DWA, let alone the connectors rusting). If you have EWS II should be another module sandwiched in between the seat support and the rear power distribution box, you can only see it when you unbolt the plastic 10mm nuts holding the distribution box and pull it back out a little to find see where the antitheft/alarm module is hiding. It is not mentioned in the official EWS technical info like this http://www.unofficialbmw.com/images/BMW_EWS.pdf

I had a later 1995 520i here for a while, it had locking and starting problems too> The wipers, radio and windows, may have worked or not (I can't remember) but to make it lock and drive I disconnected the antitheft module. I never tried removing the GM.

PS. Without your supplementary wiring, do your wipers work on full speed? I have a euro 1995 540i (7/95) here with the same problems you describe, except its wipers work fine on full speed setting. I haven't tried to run it without the GM, yet. To make it run pull one of the pins high on the EWS unit (it may have been pin #8 in the blue connector, I can't remember for sure), this enables the engine to start and run. No windows, no locks, no slow or intermittent wipers. Right now, I have the interior out, and am replacing the body loom. It is taking far too long though, as I'm building a house, and that takes priority!

Thanks for correcting me Shogun. One thing very important to be clear about, apart from the crash relay and the 'submersible' 50A in line fuse in the rear footwell, is that E34 has its EWS control module by the column, beside the drivers' knee but that this relies on numerous inputs, as you can see in the EWS technical info. However many E32/E34 also have an antitheft box (as Shogun mentioned earlier to check its fuse). It is hidden by the GM power distribution box, under the rear seat and is critical to engine start. BMW troubleshooting info focused EWS generally across all chassis seems to omit this unit's input to the immobilisation system. However it provides one of the inputs that EWS module needs to allow start. I suspect that when the loom is oxidised, that and many other GM connections fail and cause these kind of massive faults.

One tip: don't go looking for an immobilisation relay, these only exist in EWS I cars. EWS II incorporated this as a smaller, more reliable relay, hidden inside the EWS module, as well as improved logic and starter motor lockout (when engine turning).

With mine, the 'protection relay' under the rear seat (rear distribution box) is activated/pulled high. I remember seeing on the schematic that this many of the the major body circuits to turn off together (wipers/windows/roof/radio, etc) . Yours is probably the same- if so, it will get warm after a while wit just the battery connected and no key inserted. So you can check it by waiting 30mins or so and simply placing your finger on top. Also the battery will run down quicker, due to parasitic drain, of course. I disconnect mine to stop that happening. What causes the protection relay to trigger is the cause of our problems; likely GM or loom-related. So my money is on the rusty wiring and connections under the rear carpet and power distribution box given that both our cars got 'very wet feet'

Thank you so much for all your input. Since you asked a lot of question, I'm gonna answer them one by one:

>Have you tried programming the key to one of the 10 key memories?
No, I've never tried this. I know there is a tutorial for this in my "very good" repair-manual. I'll give it a try.

>When was yours built?According to my VIN, my baby was built in 4/1995

>What diagnosis tool did you use? I honestly have no idea. It wasn't mine, it belongs to a friend of mine. I'll ask him what the software was.

>Have you verified the body electronics (50A) in line fuse is not hairline cracked/rusted/blown? This is not by the battery, it's under the rear footwell carpet, drivers side on a LHD V8.I found a 50a line fuse in the big wiring loom right under the windshield in the engine bay which was perfect. But I assume that it wasn't the right one. I inspected the wiring loom around the Power-Distribution-Box very thoroughly and I'm sure there was no 50a line fuse. Since they're not too small, I should've noticed it. I will give this another try, though.
I assume LHD V8 means Left hand drive with a V8 engine, right?

>One solution is to strip the seats and carpet out get a new body wiring harness from a good e34 (same build/same options) and fit that, or at least to replace the left side and everything around the rear power distribution box. Repairing the cracked/oxidised wires is fraught with pain- there are so many small connections.My dad and me did exactly this. We inspected every connection in that loom that we found. Many were corroded and we soldered them back together. This, however, had no effect. The connections were all beneath the Rear-power-distribution box and right next to the left rear seat. Are there more connections, closer to the front perhaps?

>How is the state of the power distribution connectors, especially the GM ones, under it?They all look perfect. Not a single bit of rust at the GM or RM or their connectors. We also opened both modules and they looked perfectly clean on the inside.

> If you have EWS II should be another module sandwiched in between the seat support and the rear power distribution box, you can only see it when you unbolt the plastic 10mm nuts holding the distribution box and pull it back out a little to find see where the antitheft/alarm module is hiding.This confuses me. I'm 100% sure that there are only two black boxes in the Power-box: The GM and the RM. There are also a few fuses (not many) and three relays. I'm 100% sure there is no other black box in or around there. The only other thing is the tiny blue crash sensor. We pulled the power-box out very far, btw.

>I had a later 1995 520i here for a while, it had locking and starting problems too> The wipers, radio and windows, may have worked or not (I can't remember) but to make it lock and drive I disconnected the antitheft module.Are you talking about the module under the rear seat or about the one in the steering-column?

>Without your supplementary wiring, do your wipers work on full speed?Nope, they don't work at all. Which is strange since I read in many threads that they should work on the highest setting.

Also something strange happened: I tried returning my new GM to the seller. (Of couse I said it's broken, don't blame me, I need that 40 Merkel-Dollars back). He accepted and paid me back my money. But the he did NOT want the GM back?! I suspect he might have know that it's busted, sold it anyway and now that I wanted to return it he does not bother to get it back. I think I'll try buying another one.

Today I noticed that I still have some water leaking in. The body-sealant wasn't dried properly and the water found it's way inside since it's raining 5 days a week in Germany. Thank god it's just very little. It's all so tiresome, boys...

Until then, best regards to everyone. And thank you again for all your help!

The fusible link(s) are always close to the battery. So if the battery is under the rear seat, one wire with a fusible link goes from battery under rear seat to the B+ pole and from there to the e-box. The fusible link is close to the battery under rear seat.
The other one goes from the battery to the driver side fuse/relay box under rear seat to power that.
In case the battery is in engine bay, see here http://www.bmwe34.net/E34main/Mainte...sible_link.htm
All E32 have 2 fusible links, in case of E34 it depends on the built year, and most probably engine type (I have no details on this) read this thread https://www.bimmerforums.com/forum/s...t=fusible+link
The 1995 US spec ETM unfortunately does not show the 518i, starts with 525 http://shark.armchair.mb.ca/~dave/BMW/e34/e34_95.pdf
that shows on page 0670.2-01 2 fusible links, F97 goes to B+ junction box in engine bay and from there to the front power distribution box.
and fuse F0 is 80A and goes to 0670.2-07 page , rear power distribution box. In this case the battery is probably under rear seat passenger side.

i really tried my best to find that 50a fusible link. Though I did find one, I'm quite certain that it's not the correct one. I uploaded some pictures to imgur to show you what I found.
Please report to me if the link isn't working or if the pictures got deleted (no idea how long they stay up on imgur). Anyway here's the link to the pictures: https://imgur.com/a/W9CkCA9

I the first picture you can see the location of the fusible link that I found in the engine bay. I cut open the heatshrink and checked the link: It's perfectly ok, no cracks or anything, which you can see on the 2nd and 3rd picture.
But I'm very unsure that this even is the fusible link that you've told me about. On all the pictures I saw in that one thread that shogun sent me, the 50a fusible links were always close to the battery, and they were in the wires that came directly from the battery. This one is not. Also it was in a green cable and not the typical red cables on all the pictures. Could it be that this is just the wrong fusible link?

Genphreak, you said this: "Have you verified the body electronics (50A) in line fuse is not hairline cracked/rusted/blown? This is not by the battery, it's under the rear footwell carpet, drivers side on a LHD V8."
Are you talking about the wiring loom that goes from the a pillar, drivery side to the rear-power-distribution box?
This would make sense, since that wiring loom got very wet which could have damaged the fusible link. Unfortunately I'd have to strip the interior again to check that which I can't do right now since it's cold as **** and raining all day long.

In the 4th picture you can see my power distribution box witht he approx. location of the tiny blue crash sensor. In this picture, the GM is removed. The RM is still installed. I checked thoroughly - there is no other module/ black box around there. And yes, I did thake the yellowish carpet out.